This invention relates to perfluorocarbon based polymeric release coatings and to processes for using such coatings as mold release agents.
A wide variety of molding applications require molding apparatus with surfaces which will easily release molded articles and moding materials. Polymer deposits on molding apparatus surfaces resulting from the "sticking" occurring during molding processes not only make it more difficult and time consuming to remove molded parts from said molds, but such deposits have a tendency to deteriorate and fragment, thus decreasing the quality of the surfaces of products molded therefrom.
One approach directed towards obtaining surfaces which readily release adhesives has involved the application of various hydrocarbon and silicone oils, and waxes to the surfaces of molds which are exposed to said polymer compositions. Commonly hydrocarbon and silicone oils and waxes are sprayed or wiped onto injection molding apparatus, which is then used for the molding of polymers and prepolymers. Unfortunately, it is generally the case that only one to about three injection cycles may be performed before it is necessary to retreat the mold with said nonstick agents.
Another approach for providing molding apparatus surfaces which have good release characteristics is the application of fluorinated polymers, such as tetrafluoroethylene. These types of polymers are typically applied to a surface as small solid particles or as a coating. Unfortunately, these types of polymers are typically bound to surfaces with nonfluorinated binders or by a difficult process involving sintering of the polymer particles at high temperatures.
Perfluorinated polymers are believed to release because they produce a very low critical surface tension of wetting (.gamma..sub.c). More recently, as disclosed in U.S. Pat. No. 4,344,993, a combination of a hydrophilic polymer with up to about 0.5 weight percent perfluorocarbon and crosslinked with a cyclic sulfonium zwitterion yields a surface coating having a surface tension of wetting of less than that of coatings consisting of 100 percent perfluorocarbon. Although this type of coating is useful for preventing deposits of non-aqueous polymerization reactants and products from adhering to reactor surfaces in the production of olefinic polymers, such a coating does not adhere adequately to surfaces of conventional molding apparatus when amounts of perfluorocarbon greater than 0.5 weight percent are employed.
Therefore, it is highly desirable to provide an improved coating which adheres well to a molding apparatus surface, and a process for using same which will significantly reduce the undesirable deposition of material and sticking on internal surfaces of molding apparatus by providing a low .gamma..sub.c.